1. Field of the Invention
The present invention generally relates to marine acoustic generators and methods for their operation and use. More specifically, the present invention relates to a method and apparatus to selectively cut off fluid flow to any one of an array of marine acoustic generators.
2. Description of the Prior Art
Seismic exploration of subsea formations has involved the use of a variety of differing tools and techniques. One of the most successful tools for a marine seismic exploration is the marine acoustic generator which are commonly referred to as "airguns."
In a general embodiment, the airgun comprises a body in which a shuttle reciprocates between an open and a closed position so as to define an internal cavity. Air is supplied to and pressurized within the cavity until a selected pressure is achieved. The shuttle is then released to exhaust this pressurized air into the surrounding water to create a primary pressure pulse and a series of secondary pulses. It is these pulses which are useful in seismic evaluation.
Disadvantages associated with contemporary marine acoustic generators arise when one in an array of such generators demonstrates a leakage of fluid. Such leakage distorts the signal produced by the operation of the leaking generator and other generators in the array. Accordingly, prior procedure has required that the entire array be shut down and then retrieved on the streaming vessel. It is then necessary to locate the malfunctioning device, replace or repair the generator, restream the array and then repeat the prior seismic track. For obvious reasons, such retrieval of efforts are very costly terms of lost hours and equipment charges.
Disadvantages associated with prior marine acoustic generators also included the danger associated with their disassembly and repair. In this connection, it is not always obvious that a given device still contains a quantity of pressurized fluid (water or air). As a result, attempts to disassemble the device has often resulted in injury and death as a result of accidental explosions of these devices.